Protective apparatus for materialhandling equipment



Nov. 19, 1957 N. F. AGNEW ET AL PROTECTIVE APPARATUS FOR MATERIAL-HANDLING EQUIPMENT 4 Sheets-Sheet 1 Filed Jan. 20, 1956 Nill Power Line d n mfi y m R 95 m M M Mi; mm T w Fly la.

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PROTECTIVE APPARATUS FOR MATERIAL-HANDLING EQUIPMENT Filed Jan. 20, 1956 4 Sheets-Sheet 2 1] Ore Troqgiz D? Ore Bridge Control "01 Tra smitier w uazar [\l Dz)! IDA Idi rDU ZdC n g fab m 110KB Hill Power Line INVENTORS. Norman 1*? Agnew and F Andrew .1 Sol-0125012 THEIR A T TORNIYY Nov. 19, 1957 N. F. AGNEW ET AL PROTECTIVE APPARATUS FOR MATERIAL-HANDLING EQUIPMENT Filed Jan. 20, 1956 4 Sheets-Sheet 3 SSNEQ aw Q INVENTORS. Norman 174912010 and Andrew J:

Sorensen THE IH AITTOIIIVE'Y Nov. 19, 1957 N. F- AGNEw ET AL 2,814,032

PROTECTIVE APPARATUS FOR MATERIAL-HANDLING EQUIPMENT Filed Jan. 20, 1956 4 SheetsSheet 4 INVENTORS.

Norman E Agflewand g Andra!) JSorensen kxsy-z/lw ITIEIR A TTORNE'Y United States Patent PROTECTIVE APPARATUS FOR MATERIAL- HANDLING EQUIPMENT Norman F. Agnew, Irwin, and Andrew J. Sorensen, Edgewood, Pa., assi ors to Femco, Inc., Irwin, Pa., a corporation of Pennsylvania Application January 20, 1956, Serial No. 560,417

16 Claims. (Cl. SUP-258) Our invention relates to protective apparatus for material-handling equipment. More particularly, our invention relates to apparatus for protecting against the occurrence of collisions between material-handling devices, such for example as between a boat unloader and the bucket and cab of an ore bridge, or between two traveling cranes, and also for protecting against injuries to workmen by material-handling devices.

Under operating conditions, there is a possibility of a collision occurring between the structure of a boat unloader and the bucket and cab of an ore bridge, if an attempt is made to work the boat unloader and the ore bridge within any given area of the associated ore trough at the same time. There is also a possibility of collisions occurring between traveling cranes, such for example as in a steel mill. Furthermore, men working on the power rails, or on other parts of the structure adjacent the rails over which traveling cranes move, are in danger of being injured by the cranes while the cranes are being operated.

An object of our invention is, therefore, the provision of means for protecting against the occurrence of collisions between pieces of material-handling equipment.

Another object of our invention is the provision of means for guarding workmen against injury by movable equipment.

A first feature of our invention for accomplishing these obiects is the provision of means for warning each operator when the equipment under his control approaches within a given distance of certain other equipment or of certain areas in which men are working, and also, if desired. for warning the men when movable equipment approaches within a given distance of the area in which they are working.

More specifically, this feature of our invention embodies transmitting means located on a given first material-haudling device or structure for periodically energizing receiving means on the same structure while it is farther than a given distance from a given second material-handling structure or from a given area in which men are working. Transmitting means is provided on the given second material-handling structure, or in the given area in which men are working, for continuously energizing the receiving means on the given first structure while the given first structure is less than the given distance from the given second structure or the given area in which men are working. A clear or a danger indication is provided for the operator of the first material handling structure according as the receiving means on the first material-handling structure is periodically ener gized or is continuously energized. A clear or a danger indication can similarly be provided for the operator of the second material-handling structure, and also for men working in the given area.

A second feature of our invention is the arrangement of control circuits and apparatus provided by the first feature of our invention such that a warning indication will be given in the event of faulty operation of any of various parts of the indication control apparatus.

2,814,032 Patented Nov. 19, 1957 We shall describe three forms of apparatus embodying our invention, and shall then point out the novel features thereof in claims.

In the accompanying drawings,

Figs. 1a and lb, when placed side by side, with Fig. In on the left, constitute a diagrammatic view showing one form of apparatus embodying our invention, in which a receiving loop on a boat unloader is periodically energized from a first electronic oscillator on the boat unloader, through a check transmitting loop, while the boat unloader is farther than a given distance from a given ore bridge; in which the receiving loop on the boat unloader is also continuously energized from a second electronic oscillator on the given ore bridge, through a control transmitting loop on the ore bridge, while the boat unloader is less than the given distance from the ore bridge; and in which a clear or a danger indication is provided for the operators of the boat unloader and the ore bridge according as the receiving loop on the boat unloader is periodically energized or is continuously energized.

Fig. 2 is a diagrammatic view showing another form of apparatus embodying our invention, in which a first of three traveling cranes which are operable over a given track is equipped with a first check transmitting loop for supplying energy at a first given frequency, and is equipped with a first control transmitting loop for supplying energy at a second given frequency, and is also equipped with a first receiving loop in a first receiving circuit which is responsive to energy of said first given frequency but not to energy of said second given frequency; in which a second of said three traveling cranes, or a given area in which men are working, is equipped with a second control transmitting loop for supplying control energy at said first given frequency, and is equipped with a second check transmitting loop for supplying energy at said second given frequency, and is also equipped with a second receiving loop in a second receiving circuit which is responsive to current of said second given frequency but not to current of said first given frequency; and in which the third of said three traveling cranes, or a given area in which men are working, is equipped with a third control transmitting loop for supplying control energy at said second given frequency, and is equipped with a third check transmitting loop for supplying energy at said first given frequency and is also equipped with a third receiving loop in a third receiving circuit which is responsive to current of said first given frequency but not to current of said second given frequency.

Fig. 3 is a diagrammatic view showing a modification of a portion of the apparatus of Fig. 2, in which the first and third control transmitting loops are disposed in a plane at right angles to the plane in which the second control transmitting loop is mounted; 11'] which each check transmitting loop and each receiving loop are mounted in a plane at right angles to the plane in which the adjacent control transmitting loop on the same crane is mounted; in which all control and check transmitting loops supply energy at the same given frequency; and in which each receiving circuit is responsive to current of only the given frequency supplied by only the control and check transmitting loops which are in the same plane as the corresponding receiving loop.

Similar reference characters refer to similar parts in each of the views.

Referring to Figs. la and lb, the reference character 1T designates a track over which a boat unloader, designated by the reference character U, is movable from left to right or from right to left, as shown in the drawing and as indicated by an associated arrow. Reference character 2T designates a second track, over which an ore bridge, designated by the reference character D, is movable from left to right or from right to left, as shown in the drawing and as indicated by an associated arrow.

The reference character DC designates the cab of the ore bridge. The reference character UC designates the cab of the boat unloader.

Ore is received from boats by the boat unloader U which then deposits the ore in the ore trough shown between tracks 1T and 2T. The ore is picked up and distributed from the ore trough by ore bridge D. During distribution of the ore by ore bridge D, cab DC is moved back and forth along ore bridge D toward or away from track IT, as indicated by the associated arrow.

A suitable limit switch, such for example as shown in the drawing having an operating arm W pivoted at (1, having contacts 7 and 10, is operable by an element or arm w carried by cab DC, so that when cab DC passes a given point while approaching track 1T, contacts 7 and become closed, and when cab DC passes the given point while moving away from track 1T, contacts 7 and 1! become opened.

The mill power line, shown near the lower edge of the drawing, is supplied with direct current from a suitable source, such for example as a generator G, at terminals B and N.

A check transmitter oscillator, designated by the reference character UcM, may be of any suitable design, such for example as an electronic oscillator comprising an electron tube E of the pentode type, a transformer EF, capacitors lee and Zec, and resistors ler and Zer, with operating circuits, as shown on the drawing, energized from terminals B and N. Oscillator UcM may be proportioned to supply current at any suitable frequency, such for example as on the order of 30 kilocycles per second. The output current from oscillator UcM is supplied to an amplifier designated by the reference character 2UA.

A check loop, designated by the reference character c-p, and a receiver loop, designated by the reference character rp, are mounted on the boat unloader. Receiver loop rp. a filter designated by the reference character lUL. and an amplifier designated by the reference character lUA, are included in a receiver circuit. Filter lUL is proportioned to pass current of only the same frequency as the output current from oscillator UcM. The

receiver circuit will therefore energize a first check relay, designated by the reference character lcR, in response to only current of the same frequency as the output current from oscillator UcM.

A second check relay. designated by the reference character 2cR. is controlled by a back contact 1 of relay 10R. Energization of a capacitor, designated by the reference character Inc, and of a line relay designated by the reference character ULR is controlled by a contact 3 of relay R. Relay ULR is controlled by an asymmetric unit 2m in a manner to make relay ULR slow in releasing when its energizing circuit becomes opened.

A line transmitter oscillator, designated by the reference character ULM, and controlled by relay ULR, may be of a design similar to that of the check transmitter oscillator UcM except that oscillator ULM is proportioned to supply current at a different frequency than the current supplied by oscillator UcM. Oscillator ULM may, for example, be proportioned to supply current at a frequency on the order of 4D kilocycles per second.

Current is transmitted over the mill power line from oscillator UL'Vt, then through filters 2UL and DL to amplifiers 3UA and ZDA in cabs UC and DC, respectively. Filters 2UL and DL are proportioned to pass current of only the frequency of the output current of oscillator ULM. Capacitors Zuc, 3110, and Sdc prevent the passage of direct current from the mill power line to oscillator ULM and filters ZUL and DL, respectively.

Indication control relays UKR and DKR in cabs UC 4 and DC, respectively, are energized by current from amplifiers 3UA and ZDA, respectively.

A clear indication device, designated by the reference character UGK, which may, for example, be a green lamp, and danger indication devices URK and UBK which may, for example, he a red lamp and a bell, respectively, in cab UC, are controlled by relay UKR. Similar indication devices DGK, DRK and DBK in cab DC are controlled by relay DKR.

A control transmitter oscillator on bridge D, designated by the reference character DIM, which may be similar to oscillaor UcM, supplies current at the same frequency as the output current of oscillator UcM to an amplifier IDA. A control transmitter loop, designated by the reference character tp and mounted on ore bridge D, becomes energized by current from amplifier IDA only when contact 7 is closed by limit switch arm W operated by cab DC.

A guard relay, designated by the reference character DR, is controlled by secondary Winding 9 of a guard transformer DF, the primary winding 8 of which is included in series with control transmitter loop tp. A guard indication relay, designated by the reference character HDKR, is controlled by relay DR and by contact 10 of the limit switch arm W. A capacitor 2dc, connected in multiple with the winding of relay HDKR, makes this relay slow to pick up. A guard indication device, which may, for example, be a born or a siren, designated by the reference character H, is controlled by relay HDKR.

In describing, more in detail, the operation of the apparatus shown in Pigs. in and 1b, we shall assume that, while the boat unloader U and the ore bridge D are at a safe distance apart, that is, more than feet, the circuit for energizing relay 20R becomes closed, passing from terminal B, through contact 1 of relay lcR, and the winding of relay 20R, to terminal N. Relay 2cR then closes its contact 2, thereby completing a circuit for energizing check loop cp by current from amplifier ZUA. The current now flowing in loop 0;; induces current in the receiver loop rp in the receiver circuit including filter 1UL and amplifier lUA. Relay lcR then becomes energized by current from amplifier IUA, and opens its contact l, causing relay 20R to become deenergized. Contact 2 of relay 20R then opens the circuit for loop cp, causing loop rp and relay IcR in turn to become deenergized. Relay 2cR then again becomes energized by its circuit through contact 1 of relay lcR, causing the cycle of operations just described to be repeated. It follows that relay 2cR repeatedly becomes energized and deenergized, alternately.

Each time that relay 2cR becomes deenergized, a circuit becomes completed for charging the capacitor luc, this circuit passing from terminal B, through the back contact 3 of relay 2cR, resistor ur, and capacitor Inc to terminal N. Each time that relay 2cR then becomes energized, a circuit becomes completed for energizing relay ULR by current passing from capacitor lac, through resistor ur, front contact 3 of relay ZcR, and the winding of relay ULR back to capacitor 1110. An asymmetric unit, designated by the reference character Zui, which may for example be of the well known copper oxide rectifier type, is connected across the winding of retay ULR in order to make relay ULR slow in releasing. Contact 4 of relay ULR therefore remains closed as long as relay 20R is being repeatedly energized and deenergized alternately. With contact 4 of relay ULR closed, oscillator ULM supplies current over the mill power line to arnplifiers 3UA and ZDA through filters 2UL and DL, respectively. Relays UKR and DKR are therefore energized by current from amplifiers 3UA and 2DA, respectively.

With relay UKR energized, clear indication lamp UGK in cab UC of the boat unloader is lighted by a circuit passing from terminal B, through the front contact 5 of relay UKR, and lamp UGK to terminal N. With relay DKR energized, clear indication lamp DGK in cab DC of the ore bridge is lighted by a circuit passing from terminal B, through the front contact 6 of relay DKR, and lamp DGK to terminal N. Lamps UGK and DGK remain lighted as long as the boat unloader and the ore bridge are at a safe distance from each other. While this condititon exists, there is no restriction on the operations of the boat unloader and the ore bridge.

We shall now assume that cab DC approaches track IT and passes the given point at which arm w moves arm W of the limit switch to the position in which contacts 7 and of the limit switch arm W becomes closed. With contact 7 closed, loop tp will be energized by current passing from amplifier IDA, through contact 7, and primary winding 8 of transformer DF in multiple with a tuning capacitor ldc.

If now, either the boat unloader U or the ore bridge D should approach the other too closely, that is, within a given distance on the order of 25 to 50 feet, for example, current induced in receiver loop rp by the current in loop tp will keep relay lcR constantly in the picked-up condition, so that contact 1 of relay lcR will be held open. Relay 2cR will therefore remain deener gized, and relay ULR will become deenergized. Contact 4 of relay ULR will therefore open the line circuit over which the amplifiers 3UA and 2DA are energized by current from oscillator ULM. Relays UKR and DKR will therefore be deenergized.

With relay UKR deenergized, its front contact 5 will become opened, and back contact 5 will become closed. Lamp UGK will therefore be extinguished, and the danger lamp URK will become lighted and bell UBK will be operated by a circuit passing from terminal B, through the back contact 5, and lamp URK and bell UBK in multiple, to terminal N. Similarly, with relay DKR deenergized, lamp DGK will be extinguished, and lamp DRK will become lighted and bell DBK will become operated. Thereby, the operators of the boat unloader U and ore bridge D will be warned that their own safety, as well as that of the equipment requires great caution on their part.

The arrangement of control circuits and apparatus embodying our invention provides safeguards against the possibility of failure of one or more parts, so that if such failure should occur, warning indications will be displayed in the cabs of the boat unloader and the ore bridge. While the boat unloader and the ore bridge are at a safe distance apart, that is, more than 50 feet, for example, if a failure should occur, such for example as a break in the control circuit for relay 20R, or if oscillator UcM should fail, so that relay 2cR would be constantly deenergized, relay ULR and in turn relays UKR and DKR would also be deenergized, causing the warning indications to be displayed in the cabs UC and DC of the boat unloader and the ore bridge, respectively. Also, if oscillator ULM should fail to operate properly, the warning indications would be displayed similarly in the cabs UC and DC because of deenergization of relays UKR and DKR. If a break should occur in the circuit for either relay UKR or DKR, causing that relay to be deenergized, the warning indication would be displayed in the corresponding cab.

When the apparatus is operating correctly, if the limit switch benomes closed by cab DC, so that amplifier IDA is supplying current through contact 7 of the limit switch, and winding 8 of transformer DF, the guard relay DR will become energized by a circuit including secondary winding 9 of transformer DF, and an asymmetric unit ldi. At the same time that relay DR becomes energized, a circuit is completed, passing from terminal B, through contact 1!) of the limit switch, contact 11 of relay DR, resistor dr, and capacitor 2dc in multiple with the winding of relay HDKR to terminal N. On account of relay HDKR being slow to pick up, contact 11 of relay DR will open the circuit for relay HDKR before relay HDKR can close its contact 12 which will therefore remain open. Horn H will therefore not be sounded at this time.

If, however, oscillator DtM fails to deliver suflicient current output, relay DR will not open its contact 11, and therefore relay HDKR will close its contact 12. Warning horn H will therefore be operated by the circuit passing from terminal B, through contact 12 of relay HDKR, and horn H, to terminal N. Likewise, if the frequency of the current generated by oscillator DIM should drift beyond permissible limits, then, due to the tuning of the winding 8 of transformer DF and capacitor ldc, relay DR will remain deenergized, causing horn H to be sounded.

Referring next to Fig. 2, the reference characters 1C, 2C and 3C designate a first, and a second, and a third traveling crane, respectively, all of which are movable over the same stretch of track, designated by the reference character T, from left to right, and from right to left as shown in the drawing and as indicated by the associated arrow. Any one of the three reference characters 1C, 2C and 3C may designate a given area in which men are working, instead of designating a traveling crane. It is to be understood, therefore, that the parts described as being located on any one of the cranes could instead be in a given area in which men are working.

A check loop, a receiver loop, and a control loop, designated by the reference characters lcp, lrp, and ltp, respectively, are mounted on crane 1C, or in a given area in which men are working. A check transmitter oscillator, designated by the reference character 10M and proportioned to supply current of a suitable given frequency, such for example as 30 kilocycles per second, is provided for effecting energization of loop lcp through an amplifier 1A2 and contact 18 of a second check relay 1cR2. A filter IL is proportioned to pass current induced in loop lrp by current flowing through loop lcp, of only the frequency of the current which oscillator lcM is designed to generate, to an amplifier 1A1 for effecting energization of a first check relay lcRl. Second check relay 1cR2 is controlled by a back contact 17 of relay lcRl. A capacitor 101 and an indication relay lKR are controlled by the back and front contacts 19, respectively, of relay lcRZ, similarly to the manner in which capacitor luc and relay ULR are controlled in Fig. 1a. A clear indication lamp lGK is controlled by front contact 20 of relay lKR, and a danger indication lamp lRK and a bell lBK are controlled by back contact 20.

A control transmitter oscillator, designated by the reference character 12M and proportioned to supply current of a suitable given frequency different from the frequency of the output current of oscillator lcM, such for example as 40 kilocycles per second, energizes loop ltp in series with primary winding 21 of a guard transformer IF. A tuning capacitor 1c2 is connected in multiple with winding 21 of transformer IF. A guard indication relay lDKR is controlled by secondary winding 22 of transformer 1F. Front and back contacts 23 of relay IDKR control a clear guard indication device, which may for example be a blue lamp lDK, and a guard indication bell lDBK, respectively.

A check loop, a receiver loop, and a control loop, designated by the reference characters 20p, 2rp, and 2tp, respectively, are mounted on crane 2C or in a corresponding given area in which men are working. A check transmitter oscillator, designated by the reference character 20M and proportioned to supply current of the same frequency as current supplied by oscillator ltM, such for example, as 40 kilocycles per second, effects energization of loop 20p through an amplifier 2A2 and contact 25 of a second check relay 2cR2. A filter 2L is proportioned to pass current induced in loop 2rp by current flowing in loop 2cp, of only the frequency of the current which oscillator 2cM is designed to generate, to an amplifier 2A1 for effecting energization of a first check relay 2cRl. Second check relay 2cR2 is controlled by a back contact 24 of relay 2cRl. A capacitor 201 and an indication relay ZKR are controlled by relay ZcRZ, and indication lamps ZGK and ZRK and bell 28K are controlled by relay ZKR similarly to the manner in which corresponding parts are controlled by relays lcRZ and lKR, respectively.

A control transmitter oscillator, designated by the reference character ZtM and proportioned to supply current of the same frequency as current supplied by oscillator M, such for example, as 30 kilocycles per second, effects energization of loop 2! in series with primary winding 28 of a guard transformer 2F which is provided with a tuning capacitor 2C2. A guard indication relay ZDKR is controlled by secondary winding 29 of transforemr 2F, and indication devices 2DK and ZDEK are controlled by relay ZDKR similarly to the manncr in which cor-- responding parts are controlled by secondary winding 22 of transformer 1F and by relay IDKR, respectively.

The parts and control of the apparatus on crane 3C or in a corresponding given area in which men are working are exactly similar to the corresponding parts and control of the apparatus on crane 1C, so that oscillator 32M supplies current of a frequency of 40 kilocycles per second, oscillator 3cM supplies current of a frequency of 30 kilocycles per second, and filter 3L passes current of only 30 kilocycles per second.

Under normal operating conditions, with crane 1C at a safe distance such as St} feet from crane 2C for example, relays lcRl and MR2 will be repeatedly energized and deenergized alternately in response to current supplied by oscillator lc-M, so that relay IKR will be constantly energized similarly to relay ULR as described for Fig. la, and clear indication lamp IGK will be lighted by a circuit which includes front contact of relay IKR. If crane 3C is also at a safe distance from crane 2C, relays 2cR1 and 2cR2 on crane 2C will be repeatedly energized and deenergized alternately in response to current supplied by oscillator 2cM. and relays ScRl and 3cR2 on crane 3C will be repeatedly energized and deenergized alternately in response to current supplied by oscillator 30M so that relays ZKR and SKR will be constantly energized, and clear indication lamps ZGK and 36K will be lighted.

If now, crane 1C approaches crane 2C or a corresponding area too closely, that is, within a distance on the order of to 50 feet for example, relay [CR1 will become steadily energized in response to current from oscillator ZtM, and relay Zt'Rl will become steadily energized in response to current from oscillator lrM. Relays lcRZ and Zc-RZ will, therefore, become constantly deenergized, causing relays lKR and ZKR, respectively, to also be deenergized. With relay IKR deeuergized. danger indication lamp IKR will be lighted, and bell 15K will be operated by current passing from terminal B, through back contact 20 of relay IKR. Similarly, lamp ZRK will be lighted and bell 28K will be operated because of deenergization of relay ZKR.

From the foregoing description and the accompanying drawing, it follows that relay 'lcRl becomes energized in response to only current of a frequency of kilocycles per second induced in loop lrp by current supplied by oscillators lcM and ZIM to loops lcp and Zip, respectively, relay 2cRl becomes energized in response to only current of a frequency of 40 l'LllOCYClES per second induced in loop 2rp by current supplied by oscillators 20M, UN! and 3tM to loops 2cp, lip and 3m. respectively, and relay 3cR1 becomes energized in response to only current of 30 kilocycles per second induced in loop Ilrp by current supplied by oscillators 30M and ZrM to loops 3t'p and Zrp, respectively.

In the event of any one of the indication relays lKR, ZKR and 3KR becoming deenergized because of a failure or defect in any of the parts or circuits as described for Figs. la and lb, the corresponding danger indication lamp and bell will become energized.

Each of the guard indication relays lDKR, ZDKR and 3DKR is normally energized, so that the corresponding guard indication lamps lDK, ZDK and 3DK are normally lighted. If, however, control oscillator itM, for example, fails to deliver sutficient current output, relay lDKR will become deenergized. Likewise, if the frequency of the current generated by oscillator ltM should drift beyond permissible limits, then, due to the tuning of the winding 21 of transformer 1F and capacitor 102, relay IDKR will become deenergized. With relay lDKR deenergized, guard indication lamp lDK will be extinguished, and bell lDBK will be operated.

Referring now to Fig. 3, the parts of the apparatus and the control circuits here shown are similar to those shown in Fig. 2 except that, in Fig. 2, the check and control transmitter loops and the receiver loops cp, tp, and rp, respectively, are all in the same plane, oscillators lcM, 21M and 3cM supply current of a frequency of 30 kilocycles per second, for example, and oscillators 12M, 20M and 32M supply current of a given different frequency, such for example as 40 kilocycles per second, whereas, in Fig. 3, loops ltp, 2e11, 2rp and 3m are all in a first given plane, loops lcp, lrp, 21p, 3cp and Srp are all in a second given plane at a right angle to the first plane, and all oscillators supply current of the same given frequency. such for example as 30 kilocycles per second. In the form of apparatus shown in Fig. 3, relay lcRl becomes energized in response to only current supplied by oscillators lcM and 21M to loops lcp and 2m, respectively, in the same plane as loop lrp, relay ZcRl becomes energized in response to only current supplied by oscillators ltM, 20M, and 3tM to loops lzp, 20p, and 327), respectively, in the same plane as loop Zip, and relay 3cRl becomes energized in response to only current supplied by oscillators 2tM and 30M to loops Zip and 3m), respectively, in the same plane as loop Srp.

Although we have herein shown and described only a few forms of apparatus embodying our invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

1. Protective apparatus for material-handling equipment comprising, in combination, first transmitting means located on a first material-handling device, receiving means located on said first material-handling device, coding means controlled by said receiving means for effecting periodic operation of said receiving means by energy from said first transmitting means, second transmitting means on a second material-handling device supplying a predetermined amount of energy for effecting constant operation of said receiving means only when said first materialhandling device is within a given distance from said second material-handling device, indication control means. and circuit means controlled by said receiving means for controlling said indication control means to display a clear or a danger indication in response to periodic or constant operation respectively of said receiving means.

2. Protective apparatus for material-handling equipment comprising, in combination, first transmitting means located on a first material-handling device, receiving means located on said first material-handling device, coding means controlled by said receiving means for effecting periodic operation of said receiving means by energy from said first transmitting means, second transmitting means on a second material-handling device supplying a predetermined amount of energy for effecting constant operation of said receiving means only when said first material-handling device is within a given distance on the order of 25 to 50 feet from said second material-handling device, indication control means, and circuit means controlled by said receiving means for controlling said indication control means to display a clear or a danger indication in response to periodic or constant operation respectively of said receiving means.

3. Protective apparatus for material-handling equipment comprising, in combination, a first oscillator on a first material-handling device, said first oscillator producing output current having a frequency on the order of 30 kilocycles per second, receiving means on said first material-handling device, coding means controlled by said receiving means for effecting periodic operation of said receiving means by output current from said first oscillator, a second oscillator on a second material-handling device, said second oscillator producing output current of the same frequency as the output current from said first oscillator for at times effecting constant operation of said receiving means, indication control means, and circuit means controlled by said receiving means for controlling said indication control means to provide a clear or a danger indication according as said receiving means is periodically or constantly operated.

4. Protective apparatus for a boat unloader and an ore bridge comprising, in combination, a first oscillator on said boat unloader, said first oscillator producing output current having a given frequency, receiving means on said boat unloader, coding means controlled by said receiving means for effecting periodic operation of said receiving means by output current from said first oscillator, a second oscillator on said ore bridge, said second oscillator producing output current of the same frequency as the output current from said first oscillator, said receiving means being responsive to output current from said second oscillator for effecting constant operation of said receiving means when said boat unloader and said ore bridge are within a given distance of each other, a third oscillator, said third oscillator producing output current having a different frequency than the output current from said first oscillator, a mill power line, a periodic current converting circuit means controlled by said receiving means for supplying output current from said third oscillator to said mill power line only when said receiving means is periodically operated, indication control means, a pickup circuit means for effecting energization of said indication control means by output current of said third oscillator received from said mill power line, and a clear or a danger indication displayed in response to energization or deenergization respectively of said indication control means.

5. Protective apparatus for a boat unloader and an ore bridge comprising, in combination, a first oscillator on said boat unloader, said first oscillator producing output current having a given frequency, receiving means on said boat unloader, coding means controlled by said receiving means for effecting periodic operation of said receiving means by output current from said first oscillator, a second oscillator on said ore bridge, said second oscillator producing output current of the same frequency as the output current from said first oscillator, a cab on said ore bridge movable along said ore bridge, switch means controlled by movement of said cab along said ore bridge for at times effecting constant operation of said receiving means on said boat unloader by output current from said second oscillator, indication control means, and circuit means controlled by said receiving means for controlling said indication control means to provide a clear or a danger indication according as said receiving means is periodically or constantly operated.

6. Protective apparatus for a boat unloader and an ore bridge comprising, in combination, a first oscillator on said boat unloader, said first oscillator producing output current having a given frequency, receiving means on said boat unloader, coding means controlled by said receiving means for effecting periodic operation of said receiving means by output current from said first oscillator, a second oscillator on said ore bridge, said second oscillator producing output current of the same frequency as the output current from said first oscillator, a cab on said ore bridge movable along said ore bridge, switch means controlled by movement of said cab along said ore bridge for completing a first circuit for at times effecting constant operation of said receiving means on said boat unloader by output current from said second oscillator, a guard relay, guard circuit means responsive to output current supplied by said second oscillator when said first circuit becomes closed for energizing said guard relay, a slow pickup guard indication relay, a second circuit including a back contact of said guard relay and a contact which becomes closed by movement of said cab at the same time as said first circuit becomes closed for energizing said guard indication relay, a guard indication device controlled by a front contact of said guard indication relay, warning indication means in said cab, and boat unloader circuit means controlled by its said receiving means for controlling said warning indication means in said cab to provide a clear or a danger indication according as said receiving means is periodically or constantly operated.

7. In combination, a first and a second movable device, first energy transmitting means on said first movable device, receiving means on said first movable device, second energy transmitting means on said second movable device, coding means controlled by said receiving means for elfecting periodic energization of said receiving means by energy from said first energy transmitting means, said receiving means being controlled by said second energy transmitting means for effecting constant energization of said receiving means only when said first and second movable devices are within a given distance of each other, a first and a second indication different from each other, indication control means, and circuit means controlled by said receiving means for controlling said indication control means to provide said first or said second indication according as said receiving means is periodically or constantly energized.

8. In combination, a first and a second energy transmitting means, receiving means adjacent said first energy transmitting means, coding means controlled by said receiving means for effecting periodic operation of said receiving means by energy from said first energy transmitting means, said receiving means being controlled by said second energy transmitting means only when said receiving means and said second energy transmitting means are within a given distance of each other for eifecting constant operation of said receiving means, indication control means capable of providing a first or a second indication, and circuit means controlled by said receiving means for controlling said indication control means to provide said first or said second indication according as said receiving means is periodically or constantly operated.

9. In combination, a first and a second oscillator, each of said oscillators producing output current of the same given frequency, a check transmitting loop, a receiving loop adjacent said check transmitting loop, a control transmitting loop, circuit means for supplying output current from said first oscillator to said check transmitting loop, two bodies movable relative to each other for making said receiving loop and said control transmitting loop nearer together or farther apart, coding means controlled by current induced in said receiving loop by current flowing in said check transmitting loop for periodically interrupting the output current supplied by said first oscillator to said check transmitting loop, circuit means for constantly supplying output current from said second oscillator to said control transmitting loop, indication control means, said receiving means being controlled by current periodically induced in said receiving loop by the periodically interrupted current in said check transmitting loop for effecting energization of said indication control means while said receiving loop and said control transmitting loop are more than a given distance apart and controlled by current constantly induced in said receiving loop by current in said control transmitting loop for keeping said indication control means deenergized while said receiving loop and said control transmitting loop are less than said given distance apart, and indication means controlled by said indication control means for displaying a first or a second indication according as said indication control means is energized or is deencrgized.

10. In combination, first energy transmitting means, receiving means adjacent said first energy transmitting means, second energy transmitting means, coding means controlled by said receiving means for eilecting periodic energization of said receiving means by energy from said first energy transmitting means while said receiving means aid said second energy transmitting means are farther than a given distance apart, said receiver means being constantly energized by energy from said second energy transmitting means While said receiving means and said sec ond energy transmitting means are less than said given distance apart, indication means capable of displaying a clear or a danger indication, and circuit means controlled by said receiving means for controlling said indication means to display said clear or said danger indication according as said receiving means is periodically or constantly encrgized.

11. in combination with a boat unloader and an ore bridge, a receiving loop on said boat unloader, a first electronic oscillator on said boat unloader, a check transmitting loop on said boat unloader, loop means for energizing said check transmitting loop by current from said first electronic oscillator, coding means controlled by current induced in said receiving loop by current in said chccs transmitting loop for periodically interrupting the current supplied to said check transmitting loop by said first electronic oscillator while said boat unloader and said ore bridge are farther than a given distance apart, a control transmitting loop on said ore bridge, a second electronic oscillator on said ore bridge, said receiver means being energized by current constantly supplied from said second electronic oscillator for constantly inducing current in said receiving loop while said boat unloader and said ore bridge are less than said given distance apart, indication means capable of displaying a clear or a danger indication, and circuit means controlled indirectly by current induced in said receiving loop for controlling said indication means to display said clear or said danger indication according as said current in said receiving loop is periodically interrupted or is constantly induced.

l2. Protective apparatus for a first and a second crane which are movable over the same given stretch of space, comprising in combination, a first check transmitting loop and a first receiving loop and also a first control transmitting loop on said first crane, a first check transmitting oscillator supplying current of a first given frequency to said first check transmitting loop, a first control transmitting oscillator supplying current of a second given frequency to said first control transmitting loop, first receiving means including said first receiving loop responsive to current of said first given frequency induced in said first receiving loop by current in said first check transmitting loop but not responsive to current of said second given frequency, first coding means controlled by said first receiving means for periodically interrupting the current supplied by said first check transmitting oscillater to said first check transmitting loop, a second check transmitting loop and a second receiving loop and also a second control transmitting loop on said second crane, a second check transmitting oscillator supplying current of said second given frequency to said second check transmitting loop, a second control transmitting oscillator supplying current of said first given frequency to said second control transmitting loop, second receiving means including said second receiving loop responsive to current of said s corid given frequency induced in said second receiving loop by current in said second check transmitting loop but not responsive to current of said first given frequency, second coding means controlled by said second receiving means for periodically interrupting the current supplied by said second cliccl; transmitting oscillator to said second check transmitting loop, first indication means for said first crane, first circuit means controlled by said first receiving means for controlling said first indication means to display a clear or a dc. indication according as said first receiving means is controlled by periodically interrupted current in said first check transmitting loop or l-y constant current in said second control transmitting loop while said cranes are less than a given distance from each other, second indication means for said second crane, and second circuit means controlled by said second receiving means for controlling said second indE :ntior means to display a clear or a danger indication accoi g as said second receiving means is controlled by periodically interrupted current in said second check transmitting loop or by constant current in said first conrol transmitting loop while said cranes are less than said given distance from each other.

13. Protective apparatus for a first and a second crane which are movable over the some given stretch of space, comprising in combination. a first check transmitting loop and a first receiving loop and also a first control transmitting loop on said first crane, a second check transmitting loop and a second receiving loop and also a second control transmitting loop on said second crane, said first check. transmitting loop and said first receiving loop and also said second control transmitting loop mounted in a first given plane, said first control transmitting loop and said second cliccl; transmitting loop and also said second receiving loop mounted in a second given plane at a right angle to said first given plane, a first and a second check transmitting oscillator supplying current of a given frequency to said first and second check transmitting loops respectively, a first and a second control transmitting oscillator supplying currcnt of said given frequency to said first and second control transmitting loops respectively, first coding means controlled by current induced in said first receiving loop by current flowing in said first check transmitting loop from said first check transmitting oscillator for periodically interrupting the current supplied to said first check transmitting loop by said first check transmitting oscillator, first indication means for said first crane, said first coding means being controlled by said periodically interrupted current and by current constantly induced in said first receiving loop by current in said second control transmitting loop While said cranes are less than a given distance apart for controlling said first indication means to display a clear or a danger indication respectively, second coding means controlled by current induced in said second receiving loop by current flowing in said second check transmitting loop from said second check transmitting oscillator for periodically interrupting the current supplied to said second check transmitting loop by said second check transmitting oscillator, second indication means for said second crane, said second receiver means being controlled by said periodically interrupted current in said second check transmitting loop and by current constantly induced in said second receiving loop by current in said first control transmitting loop while said cranes are less than said given distance apart for controlling said second indication means to display a clear or a danger indication respectively.

14. In combination, a first check transmitting loop and a first receiving loop and also a first control transmitting loop in a given first location on a movable device, a second check transmitting loop and a second receiving loop and also a second control transmitting loop in a given second location, said first check transmitting loop and said first receiving loop and also said second control transmitting loop mounted in a first given plane, said first control transmitting loop and said second check transmitting loop and also said second receiving loop mounted in a second given plane at a right angle to said first plane, independent coding means for supplying periodically interrupted current of a given frequency to said first and second check transmitting loops, independent circuit means for supplying constant current of said given frequency to said first and second control transmitting loops, first indication means for said movable device, first control circuit means controlled by current induced in said first receiving loop by the periodically interrupted current in said first check transmitting loop and controlled by current induced in said first receiving loop by the constant current in said second control transmitting loop for controlling said first indication means to display a first or a second given indication respectively for said movable device, second indication means for said second location, and second control circuit means controlled by current induced in said second receiving loop by the periodically interrupted current in said second check transmitting loop and controlled by current induced in said second receiving loop by the constant current in said first control transmitting loop for controlling said second indication means to display a third or a fourth given indication respectively for said given second location.

15. In combination, a first and a second energy transmitting means, receiving means adjacent said first energy transmitting means, a first relay controlled by said receiving means, a second relay controlled by a back contact of said first relay, coding means controlled by a front contact of said second relay for effecting periodic operation of said first relay in response to energization of said receiving means by energy from said first energy transmitting means, said receiving means being controlled by said second energy transmitting means for effecting constant operation of said first relay by said receiving means only when said receiving means and said second energy transmitting means are within a given distance of each other, indication means capable of providing a first or a second indication, and circuit means controlled by said second relay for controlling said indication means to provide said first or said second indication according as said first relay is periodically or constantly operated.

16. In combination, a first and a second oscillator each capable of supplying current of a given frequency, a check transmitting loop, a receiving loop adjacent and in inductive relation to said check transmitting loop, a control transmitting loop, a receiving circuit including said receiving loop, a first relay controlled by said receiving circuit, a second relay controlled by a back contact of said first relay, a control circuit for said check trans mitting loop controlled by a front contact of said second relay for effecting periodic energization of said check transmitting loop by current from said first oscillator, said first relay periodically opening and closing its said back contact alternately in response to current induced in said receiving loop by said periodic energization of said check transmitting loop, said receiving means being energized by said control transmitting loop by current from said second oscillator for inducing current in said receiving loop effective to energize said first relay to keep its back contact open only when said receiving loop is less than a given distance from said control transmitting loop, an energy storing device, a circuit controlled by a back contact of said second relay for energizing said energy storing device, a slow release relay, a circuit controlled by a front contact of said second relay for energizing said slow release relay by current from said energy storing device, and indication means controlled by said slow release relay for displaying a first or a second indication according as said slow release relay is energized or deenergized.

References Cited in the file of this patent UNITED STATES PATENTS 1,718,528 Clark et a1. June 25, 1929 1,917,243 Edwards et al. July 11, 1933 2,355,395 Rubenstein Aug. 8, 1944 2,362,918 Miller Nov. 14, 1944 2,580,155 Brannen Dec. 25, 1951 2,753,550 Treharne July 3, 1956 

